PROJECT SUMMARY Neurodegenerative diseases encompass a wide range of nervous system pathologies that are generally characterized by progressive loss of cognitive and/or motor function, memory loss and dementia. With the increasing age of the population in the United States, the number of people affected by neurodegenerative diseases is expected to triple in the coming years, with most patients afflicted with Alzheimer?s disease. Unfortunately, there are limited or no treatment options for most neurodegenerative diseases. A growing number of studies suggest that deficits in vascular function within the central nervous system can be precipitating events that initiate neurodegeneration. Normally, the blood brain barrier (BBB) protects the brain from plasma components that would otherwise lead to cellular damage. However, chronic BBB breakdown results in leakage of serum components from the bloodstream into the central nervous system. Over time, buildup of toxic metabolites leads to cellular damage and neurodegeneration. The BBB is comprised of endothelial cells surrounded by mural cells, referred to as pericytes, and astrocytes. In both mouse and humans, loss of pericyte coverage at the BBB is associated with increased vascular leakage and the formation of calcified plaques. In humans, this defect can result in reduced cognitive function and Parkinson?s disease-like symptoms. Thus, pericyte coverage is essential for maintaining BBB integrity and limiting neurodegeneration. Despite this important role, we know little concerning how the BBB pericyte lineage is established and maintained during development. This is largely due to the lack of reliable and specific markers for BBB pericytes. This knowledge gap hinders both our understanding of BBB pericyte ontogeny and our ability to specifically manipulate this essential type in experimental settings. To address these issues, we will apply genome-wide approaches using the zebrafish as a model system to identify enhancer elements that are specific to BBB pericytes. In particular, we will identify regions of chromatin in the zebrafish genome that are specifically open in BBB pericytes. We will take advantage of double transgenic zebrafish that enable enrichment of pericyte populations. By isolating pericyte nuclei from several different tissues and comparing their open chromatin profiles, it will be possible to identify elements that are putative enhancers in BBB pericytes. We will then test activity of putative BBB pericyte enhancers in zebrafish reporter assays. We will take advantage of the ability to perform in vivo reporter assays in zebrafish to assess candidate BBB pericyte-specific enhancers. Together these studies will yield novel insights into the underlying transcriptional regulatory networks that contribute to pericyte function and maintenance of the BBB.